BaBar and PEP II. Physics

Transcription

1 BaBar and PEP II BaBar SVT DCH DIRC ECAL IFR Trigger Carsten Hast LAL Orsay December 8th 2000 Physics Main Goal: CP Violation sin2β,sin2α PEP II Performance Backgrounds December 8th 2000 Carsten Hast PEP II Operation 1

2 Unitary Triangle B d D * π, Β Κπ December 8th 2000 Carsten Hast PEP II Operation 2

3 CP Violation in B 0 J/ψ K 0 S Unmixed Decay B 0 b d d Mixed Decay t B 0 B 0 t b CP Violation in the Interference of B 0 J/ψ K 0 S and B 0 B 0 J/ψ K 0 S b c c J/Ψ s d K 0 S c c s d J/Ψ K 0 S Count number of B/B J/Ψ K 0 S Decays Tag the flavor (B or B decay) December 8th 2000 Carsten Hast PEP II Operation 3

4 The Golden Decay: B 0 ->J/Y K 0 s The charge of the tagging particles determines the flavor of the B Mesons December 8th 2000 Carsten Hast PEP II Operation 4

5 Tracking and VERTEXING December 8th 2000 Carsten Hast PEP II Operation 5

6 Particle ID: DIRC DCH (de/dx) December 8th 2000 Carsten Hast PEP II Operation 6

7 Lepton ID: EMC IFR December 8th 2000 Carsten Hast PEP II Operation 7

8 The BaBar Detector December 8th 2000 Carsten Hast PEP II Operation 8

9 The BaBar Detector IFR Magnet 1.5T DIRC e + e SVT DCH ECAL DIRC PhotoTubes December 8th 2000 Carsten Hast PEP II Operation 9

10 Silicon Vertex Tracker (SVT) 5 Layers 300 mm double sided Silicon 150 k channels Digital Readout intrinsic resolution 10 mm Acceptance down to 20 o December 8th 2000 Carsten Hast PEP II Operation 10

11 SVT Original and... Converted Photons December 8th 2000 Carsten Hast PEP II Operation 11

12 Silicon Basics Charged particles ionize material Reverse bias diode to collect electrons, holes December 8th 2000 Carsten Hast PEP II Operation 12

13 Vertexing Performance vertexing of πk-->d 0 vertex D 0 with beam spot = IP = D* force π soft to D* vertex and recompute p December 8th 2000 Carsten Hast PEP II Operation 13

14 Drift Chamber (DCH) 40 Layers Accuracy mm December 8th 2000 Carsten Hast PEP II Operation 14

15 DCH Reconstruction Charged particle ionizes gas HV between wires separates charges ions ionize gas, produce avalanche December 8th 2000 Carsten Hast PEP II Operation 15

16 DCH Installation December 8th 2000 Carsten Hast PEP II Operation 16

17 Tracking Performance Compare transverse momentum difference of tracks in e+e- µ+µevents need to account for the sideways PEP-II boost Measurement dominated by DCH point resolution TDR expectation: 0.3% pt December 8th 2000 Carsten Hast PEP II Operation 17

18 SVT-DCH alignment: Time dependence June 28 SVT X-position Y-position Z-position Access 300 µm 80 µm 180 µm 500 µm July 7 SVT mounted on PEP-II beamline, not on BaBar Earthquake protection SVT moves together with PEP-II DCH moves together with the rest of BaBar Day-Night variations observed in alignment correlation with position sensors temperature induced Need Rolling Calibration December 8th 2000 Carsten Hast PEP II Operation 18

19 Rolling Calibration Bhabha mass resolution (approx) (GeV) After-access jump BaBar access Manual alignment correction Rolling calibration activated December 8th 2000 Carsten Hast PEP II Operation 19

20 SVT DCH Global Alignment long term variation diurnal effect December 8th 2000 Carsten Hast PEP II Operation 20

21 Beam Spot Don t move it more than µm/hour December 8th 2000 Carsten Hast PEP II Operation 21

22 The Beam Pipe December 8th 2000 Carsten Hast PEP II Operation 22

23 Radial Distribution December 8th 2000 Carsten Hast PEP II Operation 23

24 de/dx in DCH and SVT DCH DCH SVT s =15% Nearly at Design December 8th 2000 Carsten Hast PEP II Operation 24

25 DIRC Detection of Internally Reflected Cherenkov Light December 8th 2000 Carsten Hast PEP II Operation 25

26 DIRC Reconstruction 30 photons/track Reconstruct C-angle for each PMT and each track (16 ambiguities/track) typically 4 reasonable fit C-angle for all December 8th 2000 Carsten Hast PEP II Operation 26

27 DIRC Performance Θ c D 0 K - π + December 8th 2000 Carsten Hast PEP II Operation 27

28 Electromagnetic Calorimeter (EMC) ~6500 CsI(Tl) Crystals ~18 X 0 Readout by PIN Diodes inside of Magnet December 8th 2000 Carsten Hast PEP II Operation 28

29 Electromagnetic Showers Photon, electron, positron start to shower when entering matter We measure the light December 8th 2000 Carsten Hast PEP II Operation 29

30 EMC Performance E/P for Bhabhas π 0 mass in data Energy threshold for readout at 1 MeV December 8th 2000 Carsten Hast PEP II Operation 30

31 Muon Chambers (Instrumented Flux Return IFR) Iron Plates 2-10 cm (= 65 cm) Up to 21 Layers of RPCs (Resistive Plate Chambers) 2300 m 2 of Detectors operated at 8 kv Measuring Space Points December 8th 2000 Carsten Hast PEP II Operation 31

32 Muon Chamber Performance > 95 % Chambers Working Single Layer Efficiency on Average > 75 % (was > 90 %) (goes down by 1%/month) Muon ID Efficiency ~ 80% Pion Fake Rate ~ 5 % Muon Id needs substantial improvement (which is underway...) ( we might build a new one ) December 8th 2000 Carsten Hast PEP II Operation 32

33 J/Y (and K 0 S )Reconstruction J/Y e+e - J/Y m+m - p + p - K 0 S p 0 p 0 December 8th 2000 Carsten Hast PEP II Operation 33

34 Event Display December 8th 2000 Carsten Hast PEP II Operation 34

35 PEP II Interaction Region December 8th 2000 Carsten Hast PEP II Operation 35

36 Background Issues SVT radiation damage (< 2 MRad/10y) SVT occupancy The issues Drift chamber occupancy Aging Lvl-1 trigger rate < 1-2 khz CsI calorimeter rad. Damage (<10kRad/10y) Readout and Occupancy Limits DCH electronics: radiation damage Current(< 20 & krad/10y) luminosity limits December 8th 2000 Carsten Hast PEP II Operation 36

37 SVT Background Event Bunch-xing : 4.2 nsec Trigger window: 1-2 usec ~ 230 Crossings / Trigger December 8th 2000 Carsten Hast PEP II Operation 37

38 Background in the SVT Little hole in Tantalum shielding December 8th 2000 Carsten Hast PEP II Operation 38

39 SVT Radiation Extrapolations get lower and lower! That s Great! December 8th 2000 Carsten Hast PEP II Operation 39

40 SVT P-Stop Shorts Acute radiation blast bias voltage drops across AC decoupling capacitors and can break the weak ones pinholes and p-stop shorts creation dead channels distortion of the electric field close to the fault December 8th 2000 Carsten Hast PEP II Operation 40

41 SVT Operation cont. Bias Current Monitoring 4 P-Stop Shorts in one special incident October 1999 where PEP lost high amount of beam in BaBar and the beam dump came too late (reason unknown) July 2000: 6-9 PSS due to LER Q4R magnet trip October 2000: Increase of leakage currents correlated with magnet trips (no PSS strange..) In Layers 1 and 2 we see them immediately Please: Don t Do that too often!!!!!!!!!!!!!!!!!!!!!!!! December 8th 2000 Carsten Hast PEP II Operation 41

42 SVT Radiation Budget Budget: 2 Mrad / 10 years Lumi: 300fb / 10 y 1. Year: 10% Radiation 1 % Luminosity 2. Year: 20 % Radiation 8 % Luminosity We re doing fine December 8th 2000 Carsten Hast PEP II Operation 42

43 DIRC Background Scrubbing Behavior Dead time if rate > 200kHz July was perfect! December 8th 2000 Carsten Hast PEP II Operation 43

44 DCH Background DCH Trips/Day during 2000 Each trip takes 2 minutes High DCH currents shorten DCH lifetime High backgrounds will degrade reconstruction efficiency December 8th 2000 Carsten Hast PEP II Operation 44

45 EMC Background Radiation levels are ok Cluster Occupancy X-tal Occupancy Occupancies are adjustable, but cost reco efficiency December 8th 2000 Carsten Hast PEP II Operation 45

46 Trigger Rates Trigger Rates were sometimes very high during 99 In 2000 things were mainly ok December 8th 2000 Carsten Hast PEP II Operation 46

47 Background Projections SVT 1900V Looks ok At higher V looks not so good December 8th 2000 Carsten Hast PEP II Operation 47

48 Background Projections DIRC Trigger Problems until 2002 Ok, but upgrade needed December 8th 2000 Carsten Hast PEP II Operation 48

49 EMC Background Prediction Occupancy Number of Clusters > 10 MeV Can be adjusted: Efficiency costs depends on physics channel December 8th 2000 Carsten Hast PEP II Operation 49

50 Summary 1. PEP II operation is excellent Record hunts are sometimes scary 2. BaBar isn t doing bad either We only have one SVT and one DCH ( for the time being) Please be careful We are all looking forward to having another fun year with incredible good performances December 8th 2000 Carsten Hast PEP II Operation 50